The invention relates to a method and apparatus for winding fiber webs, particularly partial paper and board webs, into partial web rolls, in which method, partial web rolls are wound via a nip between a winding roll and the partial web roll being formed on a winding station in connection with the winding roll.
It is known that a fiber web, e.g. paper, is manufactured in machines which together constitute a paper-manufacturing line which can be hundreds of meters long. Modern paper machines can produce over 450,000 tons of paper per year. The speed of the paper machine can exceed 2,000 m/min and the width of the paper web can be more than 11 meters.
In paper-manufacturing lines, the manufacture of paper takes place as a continuous process. A paper web completing in the paper machine is reeled by a reel-up around a reeling shaft, i.e. a reel spool, into a parent roll the diameter of which can be more than 5 meters and the weight more than 160 tons. The purpose of reeling is to modify the paper web manufactured as planar to a more easily processable form. On the reel-up located in the main machine line, the continuous process of the paper machine breaks for the first time and shifts into periodic operation.
The web of the parent roll produced in paper manufacture is full-width and even more than 100 km long so it must be slit into partial webs with suitable width and length for the customers of the paper mill and wound around cores into so-called customer rolls before delivering them from the paper mill. This slitting and winding up of the web takes place as known in an appropriate separate machine, i.e. a slitter-winder.
On the slitter-winder, the parent roll is unwound, the wide web is slit on the slitting section into several narrower partial webs which are wound up on the winding section around winding cores, such as spools, into customer rolls. When the customer rolls are completed, the slitter-winder is stopped and the wound rolls (i.e. the so-called set) are removed from the machine. Then, the process is continued with the winding of a new set. These steps are repeated periodically until paper runs out of the parent roll, whereby a parent roll change is performed and the operation starts again as the unwinding of a new parent roll.
Slitter-winders employ winding devices of different types depending on, inter alia, the type of the fiber web being wound. On slitter-winders of the multi-station winder type, the web is guided from the unwinding via guide rolls to the slitting section where the web is slit into partial webs which are further guided either from above or from below to the winding roll/rolls of the winding stations to be wound up onto cores into customer rolls. Adjacent partial webs are wound up on different sides of the winding roll/rolls. Multistation winders have one to three winding rolls and in them each partial web is wound to a partial web roll in its own winding station. During winding a winding nip is formed between the winding roll and the partial web roll to be wound.
In winding the winding nip between the partial web roll to be wound and the winding roll tightens the web in the area of the nip. If the nip load is uneven in width of the partial web roll i.e., in the axial direction of the partial web roll, the web tightens unevenly and causes creases and wrinkles at the bottom of the partial web roll. This problem is very difficult in winders with soft winding rolls i.e., winding rolls that have a surface layer of soft coating material.
Some multistation winder types of prior art are disclosed in patent publications U.S. Pat. Nos. 3,792,824, 5,405,099, 6,012,673, 4,550,887, 4,601,435, and EP 0711245. In these prior art arrangements the partial web rolls are wound on the upper half of the circumference of the winding roll, except in the arrangement of U.S. Pat. No. 3,792,824 in which the partial rolls are wound at the side of the winding roll. In these prior arrangements winding stations are equipped with center drives, which are used during winding.
Multistation winders may also comprise rider rolls that are used for creating further load at the beginning of the winding against the winding roll and for preventing the cores from bending. The rider rolls are used to create a uniform nip load and for avoiding too high loading of core chucks used for attaching the ends of the cores at the ends of cores/partial web rolls, which would cause problems in the bottom of the partial web rolls i.e., in the beginning layers of the partial web roll to be wound, which problems are common in winding.
In winding when the partial web roll has achieved enough stiffness the influence of the rider rolls decreases. In prior art arrangements typically the loading of rider rolls can be used up to certain diameters of the partial web rolls, usually up to the diameters of 250-450 mm.
In prior art arrangements the multistation winders have typically been provided by a center drive system connected to the core chucks, whereby the torque of the core chucks has been used to tighten the web to be wound on the partial web roll. It is known that by constant center torque the circumferential force is inversely proportional to the diameter of the web roll and thus it decreases as the diameter of the web roll increases. The endurance ability of the cores limits the torque transmittable from the chucks and thus the center torque is limited in its ability to control/adjustment of the tightness of the partial web roll.
From the prior art is also known multistation winders in which rider roll devices with integrated extra drives are used for creating surface traction effective on the surface of the partial web roll. In these prior art arrangements it has been possible to partially control/adjust the tightness of the partial web roll to be wound by this surface traction of the rider rolls. This kind of prior art arrangement is disclosed for example in EP patent 0711245, in which the rider rolls are in the beginning of the winding used for loading and supporting of the partial web roll to be wound and as the winding proceeds the rider rolls are moved downward along a part in direction of the circumference of the web roll and at the end of the winding the rider rolls support the web roll to be finished from below. In this prior art arrangement the surface traction can be used during the whole winding process. This winding arrangement is as a constructional structure, expensive and the rider rolls can be used for loading only up to the web roll diameters of about 450 mm. Also the surface traction needs to be limited at the stage, when the rider rolls are at the side of the partial web roll when moving along the circumference of the web roll to the, from below, supporting position.
In prior art multistation winders U.S. Pat. Nos. 3,792,824, 5,405,099, 6,012,673, 4,550,887 and U.S. Pat. No. 4,601,435 the rider rolls have no separate drives thus surface traction cannot be used.
In prior art arrangements of multistation winders of the type disclosed in U.S. Pat. No. 4,601,435 the rider rolls move some way in linear path before the rider roll beam supporting the rider rolls is lifted up but as in these types of multistation winders the center of the partial web roll to be wound moves a curved path due to pivoted winding arm i.e. the winding nip between the partial web roll and the winding roll moves during winding on the circumference of the winding roll downwards, the movement direction and movement area of the rider rolls must be optimized to be used at the most important stage of winding, i.e. at the beginning of the winding.
It has proven that discontinuing the loading of the rider rolls at this early stage causes problems and there would be a need to use the loading of the rider rolls during a longer period of the winding. It would be very advantageous if the loading of the rider roll could be used during the whole winding period of the partial web roll, especially in connection with certain fiber web grades, for example.